Explanation:

- Let's calculate the total interest paid over four years to understand the loan amount.

- Year 1: The interest rate is 5% per annum.

- Year 2: The interest rate increases to 5.5%.

- Year 3: The interest rate becomes 6%.

- Year 4: The interest rate rises to 6.5%.

- Total Interest Calculation:

- Year 1 Interest = Principal × 5%

- Year 2 Interest = Principal × 5.5%

- Year 3 Interest = Principal × 6%

- Year 4 Interest = Principal × 6.5%

- Total Interest = Rs 4,600

- Let’s denote the principal as P.

- The equation becomes:

\(P \times (0.05 + 0.055 + 0.06 + 0.065) = 4,600\)

- Simplified, \(0.23P = 4,600\)

- Solving, \(P = 4,600 / 0.23 = Rs 20,000\)

- Option 1: Rs 20,000 is therefore correct.

Correct Answer: Rs 20,000